The invention relates to an illumination apparatus for a transparent liquid contained in a container transparent to the irradiation used and of which the lateral walls are parallel to the longitudinal axis for the purposes of control. It is particularly concerned with checking food liquids, injectable solutions and pharmaceutical preparations which are provided in particular in the form of bottles or ampoules of injectable product.
The check consists in detecting the presence of any solid particles in suspension, either natural or generated in the liquid product.
It is carried out generally by illuminating the liquid starting from a source of light placed laterally or at the base of the container. The observation can take place along the axis from the source, the occultation of a fraction of the light by the particles giving rise to their detection. Alternatively it can be carried out by observing along an axis different from that from the source to see reflections, refractions or diffractions stimulated by any particles present.
In the case of illumination through the base, known apparatus generally uses a light source and means allowing the light to penetrate through the base of the container. However these known apparatus have several disadvantages connected with the fact that they do not take account of the deformation of the light beam by the container itself. In effect the walls of the container behave as air liquid lenses which modify the beam of light; for example they make it converge or diverge, in particular as a function of the curvature of the walls. A luminous beam of light results which is deformed by the wall of the container, which does not illuminate the liquid to be checked in homogeneous fashion, that is to say the illumination produced in the body of the liquid varies from one point to another. In addition, these known apparatus illuminate without any distinction the container and the liquid. As a result of this, faults or writing which may be present on the walls of the container and which may thus be illuminated are a source of detection errors, these faults interfering with the luminous beam in the same way as the particles in suspension in the liquid and thus being confusable with them. The elimination of these erroneous detections can be obtained by lowering the level of illumination produced by the source, but this, as a result, diminishes in substantial fashion the luminous signals emitted by the particles and serving for their detection.